The standard coupling between railroad cars must be capable of withstanding the maximum tensile force exerted on any coupling in a given train. (a) If a locomotive is pulling ten cars and speeding up, on which coupling is the greatest tensile force exerted? (b) Is this tensile force due to stretching or compression? (c) If the locomotive is slowing the train down, on which coupling is the greatest tensile force exerted? (d) Is this tensile force due to stretching or compression?